Solubilized cellulose and method of making



Patented Sept. 5, 1944 Sidney M. Edelsteln, Elizabeth, N. J.

No Drawing. Application April 20, 1943, Serial No. 483,817

9 Claims.

This invention relates to solubilized cellulose and the method of makingit.

This application is a continuation in part oi my copending applicationSerial No. 407,445, filed August 19, 1941, and issued on June 22, 1943,as Patent No. 2,322,427, for Cellulose product. In this copendingapplication there is disclosed a process of dissolving cellulose insodium zincate the exact nature depending somewhat on the proportion ofcellulose used. In any case, the product is more suggestive ofundissolved cellulose than ofa solution of cellulose. On dilution of thesolution and consequent decrease of ion concentrations; the fact thatthe cellulose is solubilized first appears, the cellulose thendissolving.

solution at low temperatures, as, for exampe, at

temperatures not substantially above C.

I have now found that a solution may be efiected by sodium zincatesolution at much higher temperatures, provided the cellulose iscontacted initially with a high concentration of th zincate solution andthe resulting mixture is then diluted as by the addition of water, iceor a dilute solution of sodium zincate.

Briefly stated, the invention comprises the method of and the productresulting from contacting a cellulosic material of kind described withan aqueous solution of'sodium zincate of high concentration, so that thezincate solubilizes the cellulosic material but the cellulosic materialdoes not dissolve in the presence 01' the high concentration oi' zincatepresent, and then treating the product so as to decrease the zincateconcentration and cause the solubilized cellulose to dissolve.

The product of the invention is-used in applying cellulosic coating tovarious products, as, for example, as described in my copendingapplication. The product maybe used also as an adhesive and as aspinning solution for the manufacture of threads and sheets by usualtechnic for making thread and sheeting of regenerated cellulose. r

The mechanism .by which the higher concentration of sodium zincate usedprevents solution of the cellulosic material solubilized by the zincateis herein sometimes referred to as salting out." It is known from thedisclosure of my copending application, that a solution of cellulose ina zincate solution undergoes precipitation of cellulose when there isadded to the solution a large proportion of salt or like material that,when dissolved in water, is highly ionized.

I have now discovered that strong (highly concentrated) sodium zincatesolutions convert cellulose or like celluloslc material to soluble form,

that is, solubilizes it even at ordinary or somewhat highertemperatures. The solubility is not As the cellulosic material to besolubilized, there isused to advantage wood pulp, of which sulfite woodpulp is a satisfactory example, cotton linters or purified linters,,rayon in fioc or fibrous form,

like cellulosic material, or an alkali-stable cellulose derivative suchas one of the common cellulose ethers. Examples of the ethers that maybe used are the methyl, ethyl, hydroxyethyl, and glycolic acid ether ofcellulose. The cellulose used initially may be modified or even furtheraltered to the condition known as degraded cellulose. Also, the

, modifying or the degrading may be effected as an initial step in myprocess, as, for example by heating unmodified cellulose to 50 C. or sowith a strong solution of sodium zincate. V

In one embodiment of the invention, the cellu-' lose in selected form,say wood pulp sheets, may be wet with about an equal weight of thestrong zincate solution and the resulting solubilized product sold inthat form for subsequent dilution Just previous to or at the time ofuse.

satisfactory results with out fibers of such fine-' ness as to passlargely through a 20 mesh and preferably in major proportion throughscreens as fineas 100 mesh.

readily evident, however, since at the ionic con- The cellulose is usedin proportion to give the desired concentration in the finishedsolution. Thus, cellulose is ordinarily used in the proportion of about1 to 10 parts for parts of all ingradients including the water addedinitially with the strong solution of zincate and later as the iondiluting medium. Proportions of cellulose much below 1% in the finishedsolution give solutions' too thin for most cases, whereas concentrationsabove 10% are so viscous as to make manipulation difiicult during theforming or use of the solutions. I

The zincate used may be sodium or potassium zincate. Since sodiumzincate is entirely satisfactory and less expensive than the potassiumsalt, sodium zincate is preferred,

The zincate should contain an excess of sodium hydroxide or other alkalimetal hydroxide over the amount required theoretically to convert thezinc to zincate. Since the equivalent proportions of sodium hydroxideand zinc oxide are approximately 40 and 40.7, respectively, theproportion of the hydroxide used by weight should be in excess of thezinc oxide. Proportions of sodium hydroxide to zinc oxide that may beused are preferably about 2 to 5 parts of sodium hydroxide to 1 part ofzinc oxide by weight. Satisfactory results, particularly when solutionis effected under especially favorable condition as to temperature andkind of cellulose used, are obtained when the proportion of zinc oxideused is less than 1, say within the range of about 0.1 to 1 part.

The concentration at which the zincate is initially contacted with thecellulose to give the solubilizing effect may be varied somewhat withthe kind of cellulose used and other conditions of. the treatment. Theconcentration that is preferred is about 25 to 50 parts of zincate,figured as dry weight of the raw materials sodium hydroxide and zincoxide, for 100 parts of the aqueous solution. Proportions up to thesatura tion amounts are satisfactory, although as the zincate solutionbecomes too concentrated mechanical difficulties are introducedparticularly in establishing thorough contact of, the viscous solutionor mass with the selected cellulose. Concenerations below 25 partsof thezincate may be used, say down to a proportion corresponding to about 12parts of total sodium hydroxide in 100 parts of the solution. For bestresults as to speed of solution and uniformity of product, however, thecontent of sodium hydroxide in the solution should be not substantiallyless than 15- parts to 100 parts of the solution contacted with thecellulose and may range from this point up to the saturation proportionof some ingredient of the zincate solution. Ordinarily, there is used aconcentration of the sodium zincate solution that is so high as to causeprecipitation of cellu- I lose if such a concentration of the zincate isestablished in a previously made solution of cellulose in sodium zincatesolution of relatively low concentration. When the effect of continuousdilution during the dissolving period'is desired, without the feature ofdissolving the cellulose in the absence of cooling, then a lowerconcentrationof sodium hydroxide may be used, as, for example, theconcentration of 8 to 15% given in the table on page 1 of my saidpatent.

The zincate solution itself is first prepared by mixing zinc oxide (thisterm including the hydroxide or a zinc salt that is soluble in excess ofaqueous sodium hydroxide solution) with an excess of such solution or inother conventional manner.

The temperature of contact 01' the strong zincate solution with thecellulose may be any one at which the zincate solution solubilizes thecellulose, as determined by removal'of a portion of the treated batchand diluting with 2 or 3 times its weight of water. In general, thelower the concentration of sodium hydroxide used and the more nearly thecellulose selected approaches the completely unmodified form, the loweris the temperature required to effect a solution. With unmodifiedcellulose there may, however, be used initial temperatures ranging, say,from about 5 C. to as high as 50 C. or so; at such temperature, thestrongly alkaline zincate solution causes a degrading action. When thisdegrading has been effected, say, after an hour or so, the temperatureis lowered as by the addition of cold water.

Examples of temperatures that meet these general requirements and may beused are temperatures ranging from about 10 to 35 C. al-

though any temperature between the initial temperature of degrading andthe low temperature at which the solution undergoes crystallization ofan inorganic component thereof, as by partial In the contact of thestrong zincate solution with the cellulose before the dilution iseffected, it is required that the contact be in effect a soaking andthat the soaking be continued until there is thorough absorption of thezincate solution or wetting of all parts of the cellulose by thesolution. This soaking is considered vto be completed when the particlesappear to be uniformly wet. Usually there is required a soaking for notless than 15 minutes and. preferably a half hour or so.

A longer soaking is unobjectionable except that in most instances thereis no substantial gain from further soaking once the zincate hascontacted and wet all parts of the cellulose used.

Using materials and conditions selected. as described above, I stir thecellulosic material thoroughly with the strong zincate solution untiluniform wetting of the cellulose is obtained. Under the usual conditionsas to proportions of cellulose, zincate, and water in this initialmixture, the resulting mass is more or less crumbly or dough-likealthough sometimes mushy, as at lower proportions of cellulose. Theresulting mass either at that time or shortly before use of the finishedcellulose solution is then diluted by the addition of water, ice whichis allowed to melt, dilute sodium hydroxide or zincate solution, or thelike, to give the concentration of cellulose which is desired for theparticular use to which the product is to be put and also to decreasethe ion concentration to less than. the salting out concentration. Thedilution is accompanied by stirring. There results disintegration of theoriginal relatively still. or viscous mass to the form of the desiredreadily fiowable solu-- tion.

In general, the dilution to effect the solution should reduce theproportion of sodium hydroxide (including that combined in the zincate)to less than about 12 parts and preferably 5 to 10 parts for 100 of thefinished solution.

It will be understood that the invention is not limited to anyparticular theory of explanation of the exact mechanism by which theselected chemicals act to give the finished product. It is significant,however, that the cellulose which has been solubilized by contact withthe strong zincate undergoes solution, this term being used herein toinclude dispersion, if the concentration solved cellulose is decreased.Thus, the crumbly mushy or dough-like mass initially formed by contactwith the strong zincate may be mixed with water. .When this dilution islarge and there is necessarily an attendant large decrease of ionconcentration, the cellulose dissolves even though e temperature may notbe substantially changed by the dilution. Likewise, the concentratedzincate in the original treated mass may be largely removed by pressingand the remaining treated cellulose stirred into a dilute solution of,

sodium zincate containing, for instance, such an amount 01' sodiumhydroxide that, after the dilution and stirring, the concentration ofsodium hydroxide is about 2 to 5 parts or so for 100 of the solution.Under this condition also the solubilized cellulose dissolves.

The invention will be further illustrated by detailed description inconnection with the tollowing specific examples.

Example 1 Five pounds of viscose rayon doc is mixed with 44 pounds of asolution containing, that is made from sodium hydroxide 18%, zinc oxide6%, and water 76%. This mixture is agitated for 30 minutes at 25 C. then51 pounds of tap water are added and the whole stirred. This results ina clear cellulose solution.

Example 2 Six pounds of cotton linters are treated for 8 hours with 22pounds of a solution containing 37% of sodium hydroxide and 13% of zincoxide,

the rest being water, at a temperature of 80 C. and in an iron vessel.The resulting doughy mixture is then allowed to cool to 25 C. and enoughwater of dilution is added to make 100 pounds of total solution.

The clear solution so obtained is considered to be due to breaking downinitially of the molecule r or the cotton cellulose and its subsequentdissolving on adding the water of dilution.

Example 3 The procedure of Example 1 or 2 is followed except that themethyl, ethyl. hydroxyethyl, or glycolic acid ether of cellulose issubstituted pound for pound for the rayon floc or linters.

Example 4 Fourpounds of medium viscosity 'sulflte pulp are treated with22 pounds of aqueous zincate solution containing 37% of sodium hydroxideand 13% of zinc oxide for 1 hour and agitated. 22

pounds of cracked ice are added and the mixture is agitated for another15 to 30 minutes at 12 C. Water at room temperature is then added tomake 100 pounds solution.

Example 5 Ten parts of sodium hydroxide are dissolved inten parts ofwater and then three parts of zinc oxide are added, at a temperaturethat is preferably moderately elevated, say at 50 C. to

100 C., so as to cause rapid solution of the zinc oxide with theformation of sodium zincate.

The temperature of the zincate solution is made about 50 C.

To this 23 parts of zincate solution I add dry 6 parts of rayon staplefiber and stir the resulting mixture thoroughly, with cooling, to 25 G.

Then I add 46 parts of ice to the mixture and continue stirring untilthe temperature has reached approximately -3 C. and untilthe celluloseis completely dispersed. The ice in melting cools the. mixture andsupplies water so as to lower the concentration of zincatein thesolution, the lowering of the concentration being progressive as the icemelts .and the temperature falls.

I then warm the dispersion promptly to ap proximately 15 C.

An aging. reaction'takes place in the containers. The solution isallowed to stand at atmospheric temperature for about 24 hours beforeuse. Thus the solution may be aged (ripened) at about 15 to 35 C. 'for10 to 24 hours or so. During this period a change occurs that reducesthe viscosityof the solution. This aging reaction is particularlynoticeable when unmodified cellulose is the kind of cellulose dissolvedinitial- 1y, and'the cellulose solution is relatively concentrated, say5% or higher.

It will be understood also that. it is intended to cover all changes andmodifications of the example of the invention herein chosen for thepurpose of illustration which do not constitute depiartures from. thespirit and scope of the invent on.

What I claim is: 1. The method of forming a solution of a celluloslcmaterial which comprises contacting a cellulosic material selected fromthe group consisting of cellulose and alkali stable cellulose etherswith an aqueous solution of odium zincate of high concentration adequateto cause precipitation of cellulose previously dissolved in a zincatesolution, continuing the contact of the said cellulosic material andaqueous solution of sodium zincate until the cellulosic material isthoroughly wetted by the solution, and then diluting the resuitingmixture by adding water until the cellulosic material dissolves, thesaid aqueous solution of sodium zincate usedcontaining sodium hydroxidein excess or the proportion required theoretically to convert the zincto zincate.

2. The method of forming a solution or a cellulosic material whichcomprises contacting a cellulosic material selected from the groupconsisting of cellulose and alkali stable cellulose ethers with anaqueous solution of sodium zincate containing at least approximately 15parts of sodium hydroxide to of the solution, but not more than thesaturation proportion, continuing the contact of the said cellulosicmaterial and .aqueous solution of sodium zincate until the cellulosicmaterial is thoroughly wetted by the solution, and then diluting theresulting mixture by adding water until the cellulosic materialdissolves, the proportion of alkalinity calculated as sodium hydroxidein the said aqueous solution of sodium zincate being in excess of theproportion of zinc present calculated as zinc oxide.

3. The method described in claim 1, the temwhich comprises forming aslurry of cellulose in an aqueous sodium zincate solution containing anexcess of sodium hydroxide over the calculated proportion required toform the zincate, at a temperature above that at which the zincatesolution is an effective solvent for cellulose, then cooling the mixtureand progressively diluting the zincate solution as the temperature fallsto a temperature between the temperature of crystallizing of aninorganic component of the solution and about 5 C., until the celluloseis dissolved, so that the lowest concentration of the zincate solutionis present at the lowest temperature reached, and warming, the resultingcellulose solution .to a temperature between about 15 C.

and the temperature of gelation of the solution, the said aqueous sodiumzincate solution being of concentration within the range correspondingto alkalinity calculated as sodium hydroxide of at least 8% and notabove the saturation proportion of any ingredient present.

'7. In making a solution of cellulose, the method which comprisesforming a slurry of cellulose, ice and an aqueous solution of sodiumzincate containing an excess of sodium hydroxide over the calculatedproportion necessary to form the sodium zincate, the ice being used inamount to cool the mixture to a temperature between the temperature ofcrystallizing of an inorganic component of the solution and about 5 C.and serving to dilute the zincate solution progressively as thetemperature falls, so that the cellulose dissolves.

8. A solubilized but undissolved cellulosic material con'iprising'thewater-soluble product of SIDNEY M. EDELs'mm.

